import java.util.Random;

public class kaifayanzhengma {
    public static void main(String[] args) {
        char[] chs = new char[52];
        for (int i = 0; i < chs.length; i++) {
            if (i<=25){
                chs[i]=(char)(97+i);
            }else{
                chs[i]=(char)(39+i);
            }
        }
        String result="";
        Random r = new Random();
        for (int i = 0; i <4; i++) {
            int randomIndex=r.nextInt(chs.length);
            result=result + chs[randomIndex];
        }
        int number = r.nextInt(10);
        result=result+number;
        System.out.println(result);
    }
}
